This invention relates to multi stage, clam shell vacuum pumps. In particular, seal assemblies used in such vacuum pumps.
Vacuum pumps are known which are oil-free in their vacuum chambers and which are therefore useful in clean environments such as those found in the semiconductor industry. In such a manufacturing environment, if lubricants were present in the vacuum chambers, these materials could potentially back migrate into the process chamber and, in so doing, may cause contamination of the product being manufactured. Such dry vacuum pumps are commonly multi-stage positive displacement pumps employing intermeshing rotors in each vacuum chamber. The rotors may have the same type of profile in each chamber or the profile may change from chamber to chamber.
It is known to form the housing of such a multistage vacuum pump from two half-shell stator components, which define the plurality of pumping chambers and the fluid transfer channels for conveying gas between the pumping chambers. It is necessary to provide a sealing means between the two stator components in order to prevent leakage of the process gas from the pump and to prevent any ambient air from entering the pump. A line of sealant is typically provided to perform this sealing function.
In clean environments, such as a load lock application, the integrity of the sealing means is not jeopardised and so the sealing properties of the sealing means are maintained. However, in a harsh environment, such as may be found within a process pump, exposure to corrosive process gases may cause the sealing means to deteriorate. The deterioration of the sealing means leads to replacement of the sealant, thus causing costly servicing down times for the entire process. Furthermore, contact surfaces of the stator can experience corrosion, which can lead to anomalies in these surfaces such that distortion of the pump case can occur. This distortion leads to a reduction in clearance between rotating and static components that, in turn, can affect the mechanical reliability of the pump.
Conventional systems are known which introduce mechanical barriers to protect the static sealing mechanism by reducing the quantity of corrosive gaseous material that reaches the sealing means. However, compatibility must be achieved between the material chosen to form this mechanical barrier and the process gas. Furthermore, additional complexity is introduced into the system by the presence of such a mechanical barrier and such a mechanical barrier will not generally protect the contact faces of the stators.